By Max Cunningham
June 12, 2014
We continued to sample boulders in Valle de Las Morrenas, Valle Talari, where the hostel sits, and several places along Mount Chirripó’s ridgeline.
The view from the top of Mount Chirripó is spectacular. Looking out along the ridge I could see huge boulders of granodiorite produced by exfoliation, or the response of rock at the surface to the removal of ice.
The actual summit of Chirripó, however, is a very different kind of rock. I believe the peak is composed of a sedimentary rock that was melted and then fused back together as the magma that formed the granodiorite rocks moved toward the surface. This metamorphosed sandstone (meta-sandstone) is extremely hard, and resistant to weathering processes.
In the meta-sandstone near the summit of Mount Chirripó, I discovered glacial striations. These striations occur at 12,513 feet (the summit is 12,529 feet), which is a good 1,000 feet above the moraines in the upper portion of Valle de Las Morrenas.
By Max Cunningham
June 11, 2014
Mike and I hiked down 7,000 feet from Mount Chirripó to the Cloudbridge
Reserve early on the morning of June 10th to refuel and replenish supplies.
At this point, the Cloudbridge Reserve deserves a special mention. Tucked away in the forest above San Gerardo de Rivas, volunteers at the Cloudbridge Reserve work to transform old farmland into natural forest. After the cold ruggedness of the Mount Chirripó summit, the volunteers at Cloudbridge provided an exceptionally welcoming and engaging environment. Mike and I were extremely lucky to have such a supportive base camp.
I kept an eye out for interesting geomorphology as I walked along the trails of the Cloudbridge Reserve. The rivers here are particularly beautiful. The water is clear and blue, and channel beds are floored by bedrock and boulders (all granodioritic in composition, like many of the rocks atop Mount Chirripó). I was struck by the power of the local rivers; the erosional features carved into this hard, granodioritic rock were impressive.
After two days of rest and catching up on all we’d missed while isolated on Costa Rica’s highest peak, Mike and I headed back up to Mount Chirripó to continue sampling and to learn more about the processes shaping this landscape.
During our second journey, we hoped to extend our sampling range by venturing farther into glacial valleys and higher onto peaks. We targeted Valle de Las Morrenas, a valley that we knew well from our first sampling trip and that other researchers had discussed extensively.
Earlier, we sampled boulders from moraines adjacent to large lakes. This time, we targeted a steep drop-off (what we called a “lip) that occurs in the valley directly below the lakes. Looking at maps and satellite images, it appeared that the lower valley was actually a remnant cirque:
Our discovery of a large lateral moraine in the lower valley corroborated our hypothesis that a glacier produced the pronounced lip in Valle de Las Morrenas. The vegetative cover increased substantially as we moved lower in the valley, which made accessing the moraine a real challenge. After pushing through thick, woody bushes, we finally found ourselves on the crest of the moraine.
From the image it’s hard to tell, but this is actually a pretty big moraine, about 50-60 feet in height. Meandering rivers cut through cobbles along the moraine’s edge, analogous to what we saw in Sabana de los Leones, only here with water raging through the channel.
We quickly came to realize that the boulder selection on the crest of this lower moraine was a far cry from the beautiful, large, flat boulders we saw along moraines in the upper valley. Here, boulders seemed to be more deeply weathered, and more sparsely scattered.
While the lack of good boulders for sampling induced a bit of hand wringing (made worse by storm clouds quickly moving up the valley), the effectiveness of weathering on these boulders may add to the story of glaciation at Mount Chirripó. Deep weathering of boulders suggests that they have been sitting around, exposed to the atmosphere, for a long time. How long? Glaciologists have employed relative weathering techniques for centuries to estimate exposure age, but 10-Be dating will tell us for sure.
Across a mixed landscape, Au. sediba plods
Sometimes on two feet, and sometimes on four,
Munching on fruits and leguminous pods,
Nuts and some seeds … C3 foods galore!
They did have a choice (so coprolites hint);
Lush grasses, fat grazers were also around,
But in these old ancestors (destined for flint?)
New clues, new stories have just now been found.
With lasers and microscopes, old dental plaque —
Tiny, stuck phytoliths show a rich diet!
Scratched-up enamel, it all brings us back
To lives of these creatures that have long been quiet.
What wonders are learned from plaque and from feces,
History bound in compounds beneath!
So, we should say to that wonderful species:
Thanks for not brushing your teeth!
Palaeoanthropology: The ancestral dinner table, Nature, 2012
The diet of Australopithecus sediba, Amanda G. Henry et al., Nature, 2012
This is one in a series of poems written by Katherine Allen, a researcher in geochemistry and paleoclimate at the Lamont-Doherty Earth Observatory.
Kristen de Graauw and Cari Leland
Cari and Kristen here, checking in from Mongolia. This year we were invited to be instructors for the Third National Dendroecological Fieldweek, May 23-29 in Udleg, Mongolia. We arrived to Ulaanbaatar on May 20th so we were fortunate enough to have a few days to recover from some pretty terrible jetlag before beginning the fieldweek marathon. Anyone who has ever attended a fieldweek anywhere in the world knows how challenging (and rewarding!) these events can be. Our first few days of the fieldweek were spent at the NUM (National University of Mongolia) research station near Udleg, a few hours north of UB. We were so happy to see the beautiful countryside for a few days. We got to ride there in this awesome Russian vehicle, which Cari nicknamed Herbie.
The research station was a complex of buildings for housing, a kitchen, and lecture rooms. We shared a cozy room for two and enjoyed beautiful views of the valley and mountains surrounding us.
After everyone settled in, we met for the opening ceremony. Baatar gave a nice introduction of the project and the history of the CEME collaboration. There were 8 students in total, and 7 of them were female (girl power!). There was a good mix of participants; from first year undergraduates to PhD students.
After the opening ceremony we went out to the field. Baatar gave us a guided tour of all the current research projects at the station (there were many!) and the potential sites for the fieldweek. Then we gave a quick lecture on the basics of dendrochronology and headed back towards the research station to discuss potential fieldweek projects.
Day 2 at the research station was field sampling day. Unfortunately we woke up to a cold and rainy day but that didn’t stop our groups from heading out into the forest. After a long discussion we decided Cari would teach the Climate group and Kristen would teach the Ecology group. Cari’s group headed up the mountain in search of old larch and pine trees to core while Kristen’s group went to a portion of the forest that had been logged. The goal for the climate group was to find moisture-stressed trees and look at the relationship between tree rings and climate. The ecology group’s goal was to determine logging dates and the effects on surviving trees.
After one of the coldest and rainiest field days we’ve ever experienced we headed back to the field station to thaw and dry ourselves and the cores.
While we waited for the cores to dry, the students practiced skeleton plotting.
The next day we mounted the cores with glue and taught the students how to sand. They quickly learned that a well sanded core took time, patience, and persistence. At the end of the day we headed back to UB to begin laboratory methods.
Back at the university we had to hit the ground running with lab methods. The students skeleton plotted the samples from the research station one day, learned how to do the list method and measure the next day, and finally on the last day they learned how to run COFECHA and read the output files. It was challenging but everyone worked their hardest. The final day was very busy. The students were working on their presentations until the very last minute. The groups did an outstanding job presenting their projects, which made us feel so grateful for being able to teach such a bright and dedicated group of students. During the closing ceremony Baatar gave us both a really nice Mongolian tree and shrub guide book and then presented each student with a certificate of achievement. The students then gave us the most thoughtful gifts of Mongolian art and script.
By Max Cunningham
June 10, 2014
Mike, Colin and I made meticulous plans for exploring Mount Chirripó before we left New York, but on the way to the summit Mike and I saw something that made us change direction: at about 9,500 feet, a mysterious grassland beckoned beneath jagged peaks. With just one day to go before our trip back to the Cloudbridge Reserve to refuel, we decided to make an early morning trek to this unusual valley to investigate why it is so flat and devoid of vegetation.
Over the course of a beautiful, sunny day Mike and I trekked over the rugged terrain from Crestones Base Camp before reaching a sudden transition from forest to grassland. A few things struck us. First, a thin river snakes through this entire shallow valley. Around bends in the river we noticed sharply cut banks where the stream has become more powerful and eroded away the banks.
Second, we were surprised to find the stream bed completely dry. From a distance, we had expected to find a powerful body of water. In another test of our geomorphology knowledge we discovered that this dry stream bed is paved mostly in cobble-sized rocks, the type you might find on a cobblestone street except these cobbles are sharp and angular instead of smooth and rounded. Mike and I spent the morning walking the Sabena de Leones valley and the more we looked, the more baffled we remained by the processes that shaped this landscape. Why is the river bed dry and its sediment load so large and angular? We hope to find more clues in the coming week.
In the early afternoon, Mike and I stumbled on a small marker along the river channel in Spanish dated 1956. Combining our Spanish skills, Mike and I deduced that the sign commemorated the unfortunate death of a man by mountain lion, and then I realized that Sabana de los Leones translates to “Savannah of the Lions.” That’s all we needed to know before skedaddling back to the Talari Valley and the security of the Crestones Base Camp.
By Max Cunningham
June 9, 2014
During the last decade, scientists have noticed an apparent rise in catastrophic events in mountain valleys as glaciers retreat and permafrost thaws. Some evidence suggests that thawing glacial valleys are responsible for enormous, fast-moving landslides that can destabilize river dams and cause other damage. Last July, my colleague Colin Stark and others at Lamont identified one such landslide in Alaska.
The idea that catastrophic processes may become more frequent as glacial valleys warm globally is a frightening one, but further information is needed to assess the threat. I came to Mount Chirripó hoping to find evidence of past landslides. Before flying here, Stark and I used high-resolution satellite images to identify potential landslide features on Mount Chirripó. On our second day in the field, Kaplan and I tried to locate them on foot.
We found our first landslide in Valle de los Conejos, a cirque valley carved into Mount Chirripó’s southern side. Apparently, we walked right by it on our previous day of fieldwork; the trees and bushes growing amid the fallen boulders provide an excellent disguise.The glacial debris blends in almost perfectly with the hillside. To highlight it, I have outlined the scarp in red where the failure occurred, but even this image, taken more than a half-mile away, is deceiving. Mike and I spent what felt like hours whacking through thick bushes to get there. You can just make out some of the large boulders in the background.
From a distance I thought we could scale the landslide, but the house-sized blocks were too big to scramble over. During the slide, boulders stacked up on each other and formed crevasses and caves that are now covered in treacherous mats of vegetation. I suspect that pumas may sleep in the caves by day if they are able to withstand the altitude.
Mike and I traipsed around the landslide, stopping at various scarps to enjoy the views. The run-out distance appears to be only about a tenth of a mile, and the boulders are densely packed. Looking down, I got the impression that the landslide created a crevasse somewhere between 60 to 100 feet in depth. When did this major failure happen in relation to deglaciation?
Mike and I decided to use our CRN dating tools to find out. We made our way to several boulders on the east side of the landslide, where the rock is sedimentary, unlike the granodiorite found in the Valle de las Morrenas. Once again, Mike and I found bits of fine-grained quartz in the rocks, indicating we can measure their Beryllium-10 levels to understand how long this landslide has been exposed to cosmic rays. Mike and I think that the extent of weathering on these boulders is a clue to the age of the landslide: For the surface of these boulders to undergo alteration, they probably sat in the same place for a long period of time. Perhaps this landslide is indeed paraglacial, a result of glacier retreat and permafrost thaw. We hope our efforts to measure CRN production here will inform us.
By Max Cunningham
Our expedition has two main goals: assess glacial erosion features on Mount Chirripó and search for clues of the summit’s age. Were the broad, flat landscapes on Mount Chirripó formed by glacial erosion or a change in tectonic forces pushing the Talamanca Range up about 2.5 million years ago?
A chemical dating technique called Cosmogenic Radionuclide (CRN) Dating may lead us to the answer. This technique will help tell us how long ago the valleys flanking Mount Chirripó eroded, and therefore, whether Mount Chirripó’s high elevation landscape is older than 2.5 million years or whether it eroded into its current shape as recently as 10,000 years ago.
Earth is being constantly bombarded by high-energy protons and neutrons from beyond our solar system, and CRN dating exploits this process. The collision of high-energy particles and atoms in the atmosphere and on rock at Earth’s surface produces new atoms of different mass, or isotopes. Fortunately for many Earth scientists, the impact of cosmic rays and oxygen produces an extremely rare isotope of the element Beryllium: Beryllium-10. Oxygen is abundant in Earth’s crust, and quartz (SiO2) is among the most common minerals found there. When cosmogenic rays react with quartz at the surface, about six atoms of Beryllium-10 are produced per gram of quartz per year.
Measuring concentrations of Berylium-10 at the surface can potentially tell us how long the rock has been exposed to the atmosphere, and quartz is a particularly convenient mineral for measuring Beryllium-10 concentrations. Mike and I sought out glacial features with quartz-bearing rocks at Mount Chirripó with the hope of understanding whether rocks here were exposed to the atmosphere after the recent retreat of ice.
Glacial features jumped out at us during our initial tour of Mount Chirripó. We saw broad cirque valleys, floored by large lakes likely filled during glacial retreat. We also saw striated rocks and moraine ridges scattered with cobbles and boulders. In one valley, Valle de Las Morrenas, we noticed several lakes above the boulder-strewn ridges. This fits in neatly with previous observations of lakes dammed by moraines.
Because moraines are abandoned when the ice retreats, measuring concentrations of Beryllium-10 in boulders on top of moraines may give us an idea of how long ago glacial erosion happened here. After locating boulders sitting on moraines, our next step was to see what the boulders are made of.
We discovered that many are granodioritic, an intrusive igneous rock composed of the minerals plagioclase, amphibole and our good friend quartz! Next we took samples to analyze their Beryllium-10 levels in the lab later. Collecting samples is a physically rigorous process, especially in the low-oxygen, rainy conditions at 10,000 feet on Mount Chirripó. With a hammer and a chisel, and a bandanna to protect our faces from shattering rock fragments, we chipped away at the surface of the boulder, hoping to come away with about two pounds of rock to analyze.
We collected samples from boulders on two moraine crests. After months of processing, we hope to be able to describe how long ago glacial ice retreated from different parts of the valley. Calling the day a success, we hiked back through the afternoon rain to Crestones Base Camp.
By Max Cunningham
After arriving in the town of San Gerrardo de Rivas, Mike Kaplan and I immediately started gearing up for our trek to Mount Chirripó.
Our arrival here was somewhat hectic. After landing in San Jose around 10:30 a.m., we hopped a bus to San Isidro de el General, a town just west of Chirripó National Park. Winding through the rugged mountains of the Talamanca Range, we were treated to spectacular views of central Costa Rica’s countryside.
Once in San Isidro de el General, we navigated our way to the local office of Ministerio de Ambiente y Energia de Costa Rica, the government agency that provides research permits for Chirripó National Park. Our contact, Marisol Rodríguez Pacheco, showed remarkable patience with our broken Spanish and helped us pull together some final requirements for the permit.
By 5 p.m., the two of us made base camp at the Cloudbridge Reserve, above the San Gerrardo de Rivas. Founded in 2002, the Cloudbridge Reserve supports researchers in Costa Rica and works towards sustainable forest management. Volunteers at the Cloudbridge Reserve provided us with a beautiful working space and a warm place to sleep.
The weather here can be erratic. During the early morning hours the sun is intense and the sky is blue; by 1 p.m. clouds roll in. You can anticipate heavy rain from 4 to 6 every day, and nights are cold.
After taking a day to gather food supplies and find porters to help us carry heavy packs up to Mount Chirripó, Mike and I set off around 4:30 a.m. to make our way to the top of Mount Chirripó before the afternoon rain.
Travelers and locals alike warned us that the hike would be strenuous, and indeed they were correct. The trail leading to Mount Chirripó is steep and rugged (although pristinely maintained), and we gained nearly 5,000 feet in elevation over nine miles of trail.
One especially difficult aspect of our climb was the dramatic change in climate with elevation. Below 10,000 feet, we trekked through a humid, dense rain forest, but once above about 9,500 feet, the vegetation became sparse and the temperature dropped. At the summit of Chirripó, we rarely experienced temperatures warmer than 60°F.
In terms of Earth surface processes, this dramatic change in environment invokes thoughts about difference in landscape evolution: How does change in altitude, and associated changes in climate, affect erosion processes in the long term? This is just one question we hope our research can eventually inform.
After an 8.5 hour hike, we finally reached Talari Valley, a lowland about 500 feet below Mount Chirripó. We made camp at the Crestones Base Camp, a meticulously maintained hostel in the Talari Valley, near Cerro Chirripó. The Crestones Base Camp is home to many travelers seeking the thrill of climbing Mount Chirripó. Impressively, many of the hikers we encountered wake up around 2:30 a.m. to hike the remaining 5,000 feet to the peak of Cerro Chirripo to watch the sunrise over this beautiful mountain. Mike and I made no such plans, and instead rested for a busy week of fieldwork.
By Max Cunningham
I’m a graduate student at the Lamont-Doherty Earth Observatory and work in Colin Stark’s Earth Surface Processes Group. My research focuses on the role that climate plays in molding Earth’s surface, and how we can use clues carved into landscapes to learn more about climate and climate change in the past.
Since arriving at Lamont-Doherty, I’ve focused my attention on glacial valleys responding to climate change. I want to learn more about erosion in landscapes undergoing a transition from cold, frozen conditions to warm conditions. Questions about the timing of glacial retreat in the past and the erosional processes that occur as landscapes unfreeze are particularly relevant today, as glaciers around the world shrink in response to a warming global climate.
Specifically, I want to learn about the history of glacial erosion in tropical mountains. Features on many tropical peaks around the world suggest that glaciers once persisted at low latitudes, but nearly all of these places are far too warm to sustain glaciers today.
Glaciers are a crucial link between climate and erosion: They form only under very specific climatic conditions and leave very distinctive marks after they retreat. During a glacier’s lifetime, snow accumulates at high elevation and compacts into hard ice that flows downslope; at lower elevations warmer temperatures melt away layers of snow, allowing ice deeper within the glacier to move toward the surface. The total effect of compacting ice above and disappearing ice below is a “scooping” motion, and rocks caught in this “ice scoop” wear away bedrock. A combination of this rock-on-rock wear and other processes produces features unique to glacial erosion, such as circular valleys called cirques. In map view glacially sculpted valleys look like thumbprints in clay.
A somewhat startling realization is that these glacial thumbprints can be found on mountains in hot, tropical places like Costa Rica, Uganda, Kenya and Papua New Guinea. Some major questions arise: How long ago did glaciers carve out valleys in the tropics? How far down mountainsides did glaciers persist in these perennially warm regions? To start honing in on these questions, I’ll be traveling to Costa Rica’s tallest peak, Mount Chirripó, in Chirripó National Park for the month of June.
On Mount Chirripó, which rises to 12,530 feet, glacial thumbprints are clustered a few hundred feet below the summit. River profiles have a distinctive shape, exiting U-shaped valleys along gentle gradients and then breaking suddenly into a steep slope at about 6,500 feet. Waterfalls, or more technically “knickpoints,” form at this steep slope change.
Scientists have studied the unusual glacial thumbprints and clustering of knickpoints at Mount Chirripó. In 2000, researchers at the University of Tennessee identified a series of lakes that formed as a result of glacial erosion. They extracted sediment cores from the lakes and noticed a sharp transition from granular, glacially-produced sediment to organic material with depth in the core. Using 14C radiometric dating, they found that the transition occurred between 12,000 and 9,800 years ago.
Why is that important? Between 20,000 and 10,000 years ago the world was thawing out of an ice age. The 14C dates imply that glaciers persisted at about 12,000 feet at Mount Chirripó as recently as 9,800 years ago. By comparison, North America’s Laurentide ice sheet, which once extended south of New York City, retreated into Canada well before 9,800 years ago.
A 2012 study looked at Mount Chirripó from a different lens. The collision of tectonic plates in the tropical Pacific Ocean pushed Mount Chirripó to its modern elevation, but the timing of this uplift remains unclear. The 2012 study suggested that the clustering of knickpoints could reveal when tectonic uplift began.
Rapid tectonic uplift provides rivers with potential energy that expresses itself in steep slopes that slowly creep up mountainsides, creating a “wave” of erosion that travels up hillslopes. By assuming a “vertical” erosion rate, these researchers estimate that knickpoints at 6,500 feet signify tectonic upheaval that began about 2 million years ago.
The conclusions reached by these independent studies present a major conflict. On the one hand, valleys atop Mount Chirripó may have been carved by glaciers. If this is the case, the landscape must be “young,” as glacial erosion would have occurred during the last 2.5 million years. On the other hand, the valleys at high elevations at Mount Chirripó may represent a landscape that existed before 2 million years ago and rode a pulse of uplift to 12,500 feet.
In other words, two competing hypotheses have emerged: Is Mount Chirripó a sculpture of glacial erosion, or an ancient landscape perched at high elevations by tectonic forces?
My colleague Mike Kaplan and I plan to analyze evidence of past glaciation on Mount Chirripó in an attempt to test these two competing hypotheses. Using a geochemical technique called surface exposure age dating, which will allow us to measure how long rocks at the summit of Mount Chirripó have been exposed to the atmosphere, we will attempt to test how “old” the landscape is—is it relatively young, around 9,800 years old? Or does it predate a massive shift in tectonic uplift that began 2 million years ago?
Reports that a portion of the West Antarctic Ice Sheet has begun to irretrievably collapse, threatening a 4-foot rise in sea levels over the next couple of centuries, surged through the news media last week. But many are asking if even this dramatic news will alter the policy conversation over what to do about climate change.
Glaciers like the ones that were the focus of two new studies move at, well, a glacial pace. Researchers are used to contemplating changes that happen over many thousands of years.
This time, however, we’re talking hundreds of years, perhaps — something that can be understood in comparison to recent history, a timescale of several human generations. In that time, the papers’ authors suggest, melting ice could raise sea levels enough to inundate or at least threaten the shorelines where tens of millions of people live.
“The high-resolution records that we’re getting and the high-resolution models we’re able to make now are sort of moving the questions a little bit closer into human, understandable time frames,” said Kirsty Tinto, a researcher from Lamont-Doherty Earth Observatory who has spent a decade studying the Antarctic.
“We’re still not saying things are going to happen this year or next year. But it’s easier to grasp [a couple of hundred years] than the time scales we’re used to looking at.”
The authors of two papers published last week looked at a set of glaciers that slide down into the Amundsen Sea from a huge ice sheet in West Antarctica, which researchers for years have suspected may be nearing an “unstable” state that would lead to its collapse. The West Antarctic Ice Sheet is mostly grounded on land that is below sea level (the much larger ice sheet covering East Antarctica sits mostly on land above sea level).
Advances in radar and other scanning technologies have allowed researchers to build a detailed picture of the topography underlying these glaciers, and to better understand the dynamics of how the ice behaves. Where the forward, bottom edge of the ice meets the land is called the grounding line. Friction between the ice and the land holds back the glacier, slowing its progress to the ocean. Beyond that line, however, the ice floats on the sea surface, where it is exposed to warmer ocean water that melts and thins these shelves of ice. As the ice shelves thin and lose mass, they have less ability to hold back the glacier.
What researchers are finding now is that some of these enormous glaciers have become unhinged from the land – ice has melted back from earlier grounding lines and into deeper basins, losing its anchor on the bottom, exposing more ice to the warmer ocean water and accelerating the melting.
In their paper published in Geophysical Research Letters, Eric Rignot and colleagues from the University of California, Irvine, and NASA’s Jet Propulsion Laboratory in Pasadena, Calif., described the “rapid retreat” of several major glaciers over the past two decades, including the Pine Island, Thwaites, Haynes, Smith and Kohler glaciers.
“We find no major bed obstacle upstream of the 2011 grounding lines that would prevent further retreat of the grounding lines farther south,” they write. “We conclude that this sector of West Antarctica is undergoing a marine ice sheet instability that will significantly contribute to sea level rise in decades to come.”
The region studied holds enough ice to raise sea levels by about 4 feet (Pine Island Glacier alone covers about 62,000 square miles, larger than Florida). If the whole West Antarctic Ice Sheet were to melt, it could raise the oceans about 16 feet.
In the second paper, Ian Joughlin and colleagues from the University of Washington used models to investigate whether the Thwaites and Haynes glaciers, which together are a major contributor to sea level change, were indeed on their way to collapsing. “The simulations indicate that early-stage collapse has begun,” they said. How long that would take varies with different simulations – from 200 to 900 years.
“All of our simulations show it will retreat at less than a millimeter of sea level rise per year for a couple of hundred years, and then, boom, it just starts to really go,” Joughin said in a news release from the University of Washington.
Many scientists who’ve been studying the region were already braced for the storm.
“It’s gone over the tipping point, and there’s no coming back,” said Jim Cochran, another Lamont researcher with experience in the Antarctic. “This … confirms what we’ve been thinking for quite a while.”
Cochran is principal lead investigator for Columbia University in Ice Bridge, the NASA-directed program that sends scientists to Antarctica and Greenland to study ice sheets, ice shelves and sea ice using airborne surveys. Much of the data used in the new papers came from the Ice Bridge project.
Tinto, also an Ice Bridge veteran, agreed. “I thought it was pretty exciting, because we’ve all been working on this area for a long time, and that potential for the West Antarctic Ice Sheet to behave in this way, we’ve been aware of it for a long time,” she said. “[It] made me want to get in there and look at the rest of the area, what else is going on.”
And there are still many questions about what’s going on: How fast the ocean that swirls around Antarctica is warming, how those ocean currents shift, and to what extent that is influenced by global warming.
“I have a problem with the widespread implication (in the popular press) that the West Antarctic collapse can be attributed to anthropogenic climate change,” said Mike Wolovik, a graduate researcher at Lamont-Doherty who studies ice sheet dynamics. “The marine ice sheet instability is an inherent part of ice sheet dynamics that doesn’t require any human forcing to operate. When the papers say that collapse is underway, and likely to last for several hundred years, that’s a reasonable and plausible conclusion.”
But, he said, the link between CO2 levels and the loss of ice in West Antarctica “is pretty tenuous.” The upwelling of warmer waters that melt the ice has been tied to stronger westerly winds around Antarctica, which have been linked to a stronger air pressure difference between the polar latitudes and the mid-latitudes, which have in turn been linked to global warming.
“I’m not an atmospheric scientist, so I can’t evaluate the strength of all of those linkages,” Wolovik said. “However, it’s a lot of linkages.” And that leaves a lot of room for uncertainty about what’s actually causing the collapse of the glaciers, he said.
Researchers have been discussing the theory of how marine ice sheets become unstable for many years, said Stan Jacobs, an oceanographer at Lamont-Doherty who has studied ocean currents and their impact on ice shelves for several decades.
“Some of us are a bit wary of indications that substantial new ground has been broken” by the two new papers, Jacobs said. While ocean temperatures seem to be the main cause of the West Antarctic ice retreat, there’s a lot of variability in how heat is transported around the ocean in the region, and it’s unclear what’s driving that, he said. And, he’s skeptical that modeling the system at this point can accurately predict the timing of the ice’s retreat.
But, he added, “this is one more message indicating that a substantial sea level rise from continued melting of the West Antarctic Ice Sheet could occur in the foreseeable future. In the absence of serious near-term greenhouse gas mitigation efforts, such as an escalating tax on carbon, they may well be right.”
“It starts bringing it a little closer to home,” said Tinto. “It’s a significant amount of change, but something we can start planning for. Hopefully [this will] make people stop procrastinating and start planning for it.”
Cochran agreed: The papers’ message is “that … over the next couple hundred years, there’s going to be a significant rise in sea level, and at this point we can’t stop it.” But, he added, “it doesn’t say give up on trying to cut emissions. … [Just] don’t buy land in Florida.”
For further details on what’s going on in West Antarctica, check out these resources:
- A NASA primer on the West Antarctic Ice Sheet
- Images and video on Antarctica from NASA
- J Farmer’s Almanac: an explanation of the studies by Jesse Farmer, a PhD student in the Department of Earth and Environmental Sciences at Columbia University.
- An explanation on the Antarctic Glaciers.org site
- More on the Ice Bridge program
The two papers in question:
Widespread, rapid grounding line retreat of Pine Island, Thwaites, Smith and Kohler glaciers, West Antarctica from 1992 to 2011, E. Rignot, J. Mouginot, M. Morlighem, H. Seroussi, B. Scheuchl, Geophysical Research Letters (2014)
Marine Ice Sheet Collapse Potentially Underway for the Thwaites Glacier Basin, West Antarctica, Ian Joughin, Benjamin E. Smith, Brooke Medley, Science (2014)
Armin Van Buuren, Ancient Wood, and Ghengis Khan: This is not your father’s field research in Mongolia
We never expected this. Enkhbat had us hovering at warp speed along the Millennium Road in the northern shadows of the Khangai Mountains. Armin Van Buuren’s A State of Trance filling our rig. We were starting a new project to study the interaction between climate, fire, and forest history in the land of Chinggis Khaan and a silky voice was lifting us higher, “and if you only knew, just how much the Sun needs you, to help him light the sky, you’d be surprised. Do…do…do.do”. We were exhilarated. The Sun was shining. This was not exactly Chinggis’ steppe. But little did we know, we would eventually be chasing his ghost.
Byarbaatar & Amy in front of Khorgo, unknowingly about to meet Chinggis’s ghost. Photo credit: Enkhbat.
After about a day’s travel we started passing the Khorgo lava field. Amy asked, “What’s that?” Neil had forgotten about this landmark despite having walked upon it 10 years prior. It is a ~30 km2 lava field with old trees on it. Gordon Jacoby, Nicole Davi, Baatarbileg Nachin, and others had sampled in the early aughts and put together a ca 700 yr long drought record from Siberian larch. Neil relayed this information to Amy and she said that we should sample on it knowing that a 2,000 yr long record in the American Southwest had been produced on a similar landscape feature. We had a tight schedule, but as we drove out to the western edge of the Khangai’s, sampled sites, witnessed a sheep in the dying throes of a brain worm infection, got snowed on, and then sweated in much warmer temperatures, we decided it was worth the time to see what was out there. Little did we know.
By the time we arrived to start sampling, Neil was getting sick (we learned days later that Neil was coming down with tonsillitis) and we were on fumes from some bone-challenging swings in the weather. Amy pushed on during the first day with Byarbaatar and Balginnyam. The found a pile of dead horse bones and couldn’t get the chainsaw running stopping them from acquiring samples from downed, dead trees. It felt almost hopeless.
We summoned our strength the next day and explored a new section of the lava field. Soon after getting out there we starting seeing Siberian pine, a tree Neil hadn’t seen on his first visit and hadn’t been sampled previously at this site. We decided that after our fire history collection we would sample some pine trees just to see what They might have to say.
The Logo Tree: The Siberian pine that clued us into the possibility that there might be something extraordinary on the Khorgo lava field. Photo credit: Amy Hessl
As this collection wasn’t priority, these samples sat until late January of the following year. Here is the first email of the discovery (partially redacted for some sensitive language).
The sample “locked in and said the inner ring i measured was 1235…whoa! that was cool b/c i started a good bit from the pith…. i race back to me scope and measuring stage…..make mistakes. going too fast. fix the mistakes…..the PITH is 1142!!!!
yes, i can see the yr Chinggis was born. i can see the yr he died. i can see the yrs Mongolia rose to rule Asia!
this has been our Holy Chinggis during the entire Mongolian project.
this is totally hot censored.
ps – i guess we are going back to Khorgo, huh?”
KLP0010a – the first sample of Siberian pine from the 2010 Khorgo lava collection to break the 1200s. The pith is 1142 CE (Common Era). Photo credit: Neil Pederson
We secured funding and we went back to Khorgo in 2012 with a bigger crew and one goal in mind – collect more wood.
We cannot believe what we have found.
For centuries, common wisdom held that the Mongols were driven to conquest because of harsh conditions – drought. Our new record, dating back with confidence to 900 CE (Common Era), indicates the opposite. After the unification of the Mongols, Chinggis Khan, you know him as Ghengis Khan, led his army from Northern China in 1211 to the Caspian Sea in 1224 CE. Our new record in PNAS indicates that it was consistently wet from 1211-1225, a period we are calling the Mongol Pluvial (look for an open access version of this paper here or contact Amy or me). No years during this period were below the long-term average, which is a singular rare run of moisture conditions in our 1,100 year long record. Independent tree-ring records over extra tropical Asia also indicate that this period was warm.
On the cool semi-arid steppe of Central Asia, water is life and in those days, water was energy. The Mongol diet is heavily based on the meat of grazers. Their mode of transportation was the short, but Pheidippidic horse. So, for food and for travel, grass is life. Grass is energy. An abundance of moisture would seem to provide the horsepower for the rapidly growing Mongol Empire. The Mongol soldier had five steed at their disposal. With a large army, that quickly translates into a huge herd and a huge need for grass.
Our tree-ring record suggests that the grasslands of central Mongolia were likely productive. They strongly agree with satellite estimates of grassland productivity. Going back in time, then, the trees would suggest the Mongol Empire during its rapid expansion was sitting in a sea of grass, a sea of energy, a potential abundance of life.
That is our hypothesis, anyhow, and something we will test in the coming years with historical documents, environmental records from lake sediments, more tree rings, and ecological modeling experiments.
While this record speaks to a rapid transformation of Eurasian culture during the 13th century, it also speaks about an abrupt transformation in Mongol culture today. Towards the end of our tree-ring record we see a prolonged drought from the end of the 20th century into the beginning of the 21st century. This drought followed the wettest century of the last 11 and occurred during the warmest period of the last 1,100 years in Asia. The abrupt transition in the environmental conditions, a transition that saw hundreds of lakes and wetlands disappear from the landscape, occurs during the transition from a more agriculturally-based economy to a more urban-based economy. These severe conditions, in combination with some harsh winters, killed millions of livestock and are thought to be one trigger of a mass migration of Mongols from the countryside into the capital of Ulaanbaatar.
Ulaanbaatar in 2006. The homes on the far hills likely reflect climatic and economic refugees moving from the countryside into the city. Photo credit: N. Pederson
Though we cannot connect this heat drought to climate change (though maybe we kind of can), warming temperatures have stacked the deck towards higher evaporative demand, so even if the amount of precipitation remains the same, high temperatures will generate a more intense drought. That’s what we observed in the early 21st century and based on past moisture variation in Mongolia and future predictions of warming, we would expect to see similar events in the future.
From Armin Van Buuren to Chinggis Khaan to Armin Van Buuren again. We had no clue of how Summer 2010 would light the sky.*
* this post was requested by a media outlet so they could have the ‘author’s voice’ on this discovery. That version was ultimately sanitized for your protection. Here it is unadultered.
To record these lower-crustal and upper-mantle phases as “first arrivals”, where they are not obscured by the arrival of energy from shallow paths, we use long lines. Long lines mean lots of receivers and lots of driving to deploy and recover these instruments. We could have used lots of sources instead, but the blasts we used to get seismic energy into the lower crust and upper mantle in this experiment take a lot of time and money to setup. Receivers are much cheaper, so we used a lot of them. (For similar wide-angle/long-offset work at sea, airgun sources are cheaper than putting seismometers on the seafloor, so we use many shots and a smaller number of receivers out there.)
South-central part of the seismic line. The yellow line is team 5's section. We have been in a relatively rural part of Georgia and as a result have not encountered many locals save a few who have stopped to ask if we are ok. However, we have seen quite a few interesting things that are quite out of the ordinary (to me at least).
Friendly Muscovy duck.Rocks in a stream bed with associated pink spongy material (?)
Spanish moss.Linguoid (current) ripples on a washed out road. We have also seen quite a few old abandoned farm houses in various stages of aging...
All said we have dug 122 holes in team 5's stretch. We have also helped deploy instruments in other sections as well and while doing so have seen others hard at work.
Meghan and Nate getting it done!Along the way the cars have taken quite a beating and have actually held up pretty well. Although there have been a few instances where people got stuck, I think that the people with the toughest job will be the guys that have to detail the cars upon their return...
A more appropriate vehicle (?)And lastly here's a couple more random pictures that I thought were interesting.
The large disparity in fuel grade gas prices.
A ~perfectly leveled geophone (it's harder than you'd think).Hopefully this random selection of pictures was entertaining. Up next we will post about last night's "shots." In the meantime, I can say that they were all successful with varying degrees of excitement. The most important thing is that all of our hard work is being realized as the instruments are recording refractions from buried geology that will help us unravel some of the mystery that surrounds events that happened in this area long ago.
James Gibson, LDEO
into the field where they undoubtedly got a little mud on their tires.
seismograph will be installed amid the sandy surroundings of a Ponderosa Pine farm.
Adrian Gutierrez, 13 March 14
7:30 am: Leave Georgia Southwestern State University, where we are staying, and head to the site8:20 am: Arrive at site 8:30 am: Start drilling and take geological samples every 5 ft.
11 March 2014
9 March 14
Spanish moss lined trees along our transect south of Valdosta
5 March 2014